Near-critical two-dimensional smectic-C to solid-like phase transition in azobenzene-derivative Langmuir monolayers

The Langmuir monolayers of amphiphilic derivatives of azobenzene were characterized on the basis of observed two dimensional smectic-C to solid like phase transition. The loss of continuous first order transition at higher temperatures and pressures confirmed the presence of a critical point and the existence of a two dimensional hexatic-hexatic transition. The characterization was based on surface pressure and molecular area isotherms, macroscopic optical textures and grazing incidence x-ray diffraction.